Administrator Guide

ALUA Port Mode
Asymmetric Logical Unit Access (ALUA) provides port and controller redundancy for SAS front-end connections.
Volumes mapped to a server using SAS front-end also have port and controller redundancy. Volumes mapped over SAS are mapped to
both
controllers. The volume mapping is Active/Optimized on one controller and Standby on the other controller. If the port or controller
fails on the active controller, the paths to the other controller become Active/Optimized. The mapping on the first controller switches to
Standby. When the port or
controller recovers, the mapping to the first controller returns to Active/Optimized and the mapping to the
second controller returns to Standby status.
Legacy Mode
Legacy mode provides controller redundancy for a dual-controller Storage Center by connecting multiple primary and reserved ports to
each Fibre Channel or Ethernet switch.
NOTE:
Legacy mode is not available on SCv2000 or SCv3000 series Storage Centers
In legacy mode, each primary port on a controller is paired with a corresponding reserved port on the other controller. During normal
conditions, the primary ports process I/O and the reserved ports are in standby mode. If a controller fails, the primary ports fail over to the
corresponding reserved ports on the other controller. This approach ensures that servers connected to the switch do not lose
connectivity if one of the
controllers fails. For optimal performance, the primary ports should be evenly distributed across both controllers.
When possible, front-end connections should be made to separate controller I/O cards to improve redundancy.
About Fault Domains and Ports
Fault domains group front‐end ports that are connected to the same transport media, such as a Fibre Channel fabric or Ethernet network.
Ports that belong to the same fault domain can fail over to each other because they have the same connectivity.
Front-end ports are categorized into fault domains that identify the allowed port movement when a controller reboots or a port fails.
Failure modes and port activity depend on whether the Storage Center is configured for Legacy mode, ALUA port mode, or Virtual port
mode.
Fault Domains for SCv2000 Series Storage Systems
The Storage Center handles all fault domain creation and modification on SCv2000 series storage systems.
Depending on the hardware configuration, the following fault domains are automatically created on SCv2000 series storage systems:
• For SCv2000 series storage systems with Fibre Channel HBAs, two fault domains are created for the Fibre Channel ports.
• For SCv2000 series storage systems with iSCSI HBAs, two fault domains are created for the iSCSI ports.
• For SCv2000 series storage systems with SAS HBAs, four fault domains are created for the SAS ports.
• Fault domains are automatically created for Flex/Embedded Ethernet ports.
NOTE:
Additional front-end fault domains cannot be created on SCv2000 series storage systems. In addition, existing
fault domains cannot be modified or deleted on SCv2000 series storage systems.
Fault Domains for SCv3000 Series Storage Systems
The Storage Center handles all fault domain creation and modification on SCv3000 series storage systems.
Depending on the hardware configuration, the following fault domains are automatically created on SCv3000 series storage systems:
• For SCv3000 series storage systems with Fibre Channel HBAs, two fault domains are created for the Fibre Channel ports.
• For SCv3000 series storage systems with iSCSI HBAs, two fault domains are created for the iSCSI ports.
• For SCv3000 series storage systems with SAS HBAs, four fault domains are created for the SAS ports.
• For SCv3000 series storage systems with iSCSI mezzanine cards, two fault domains are created for the iSCSI ports.
• For SCv3000 series storage systems with iSCSI mezzanine cards and iSCSI HBAs, four fault domains are created for iSCSI ports
NOTE:
Additional front-end fault domains cannot be created on SCv3000 series storage systems. In addition, existing
fault domains cannot be modified or deleted on SCv3000 series storage systems.
Fault Domains in Virtual Port Mode
In virtual port mode, fault domains group front-end ports that are connected to the same Fibre Channel fabric or Ethernet network. All
ports in a fault domain are available for I/O. If a port fails, I/O is routed to another port in the fault domain.
The following requirements apply to fault domains in virtual port mode:
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Storage Center Maintenance